docs: def revert_prompt(self,
  	                  old_prompt_name,
  	                  new_expect=None):
  		"""Reverts the prompt to the previous value (passed-in).
  
  		It should be fairly rare to need this. Most of the time you would just
  		exit a subshell rather than resetting the prompt.
  
  		    - old_prompt_name -
  		    - new_expect      -
  		    - child           - See send()
  		"""
  		shutit = self.shutit
  		expect = new_expect or self.default_expect
  		#           v the space is intentional, to avoid polluting bash history.
  		self.send(ShutItSendSpec(self,
  		                         send=(' PS1="${PS1_%s}" && unset PS1_%s') % (old_prompt_name, old_prompt_name),
  		                         expect=expect,
  		                         check_exit=False,
  		                         fail_on_empty_before=False,
  		                         echo=False,
  		                         loglevel=logging.DEBUG,
  		                         ignore_background=True))
  		if not new_expect:
  			shutit.log('Resetting default expect to default', level=logging.DEBUG)
  			shutit.set_default_shutit_pexpect_session_expect()
  		_ = self.init_pexpect_session_environment(old_prompt_name)